Face perception

Face perception is the process by which the brain and mind understand and interpret the face, particularly the human face.

The face is an important site for the identification of others and conveys significant social information. Probably because of the importance of its role in social interaction, psychological processes involved in face perception are known to be present from birth, complex, involve large and widely distributed areas in the brain and can be selectively damaged to cause a specific impairment in understanding faces known as prosopagnosia.

Development of face perception

Whilst there is no question that the majority of face perception skills developed by adults are not present in babies, there is evidence of an innate tendency to pay attention to faces from birth. It is known that early perceptual experience is crucial to the development of visual perception and this orienting response undoubedtly encourages the rapid development of face specific skills such as the ability to identify friendly others and relatively complex pre-verbal communication. By two months of age face perception has developed so specific areas of the brain are known to be activated by viewing faces¹

Adult face perception

Theories about the processes involved in adult face perception have largely come from two sources; research on normal adult face perception and the study of impairments in face perception that are caused by brain injury or neurological illness.

One of the most widely accepted theories of face perception² argues that understanding faces involves several stages; from basic perceptual manipulations on the sensory information to derive details about the person (such as age, gender or attractiveness), to being able to recall meaningful details such as their name and any relevant past experiences of the individual.

This model (developed by psychologists Vicki Bruce and Andrew Young) argues that face perception might involve several independent subprocess working in unison.

A 'view centred description' is derived from the perceptual input. Simple physical aspects of the face are used to work out age, gender or simple facial expressions. Most analysis at this stage is on feature-by-feature basis.
This initial information is used to create a structural model of the face, which allows it to be compared to other faces in memory, and across views. This explains why that the same person seen seen from a novel angle can still be recognised. This structural encoding can be seen to be specific for upright faces as demonstrated by the Thatcher effect.
The structurally encoded representation is transferred to notional 'face recognition units' which in conjunction with 'person identity nodes' allow the person to be identified by information from semantic memory. Interestingly, the ability to produce someone's name when presented with their face has been shown to be selectively damaged in some cases of brain injury, suggesting that naming may be a separate process from being able to produce other information about a person.

The study of prosopagnosia (an impairment in recognising faces which is usually caused by brain injury) has been particularly helpful in understanding how normal face perception might work. Individuals with prosopagnosia may differ in their abilities to understand faces, and it has been the investigation of these differences which has suggested that several stage theories might be correct.

Face perception is an ability which involves a great deal of the brain, however some areas have been shown to be particularly important. Brain imaging studies typically show a great deal of activity in an area of the temporal lobe known as the fusiform gyrus, an area also known to cause prosopagnosia when damaged (particularly when damage occurs on both sides). This evidence has led to a particular interest in this area and it is sometimes referred to as the fusiform face area for that reason.

Controversies

Whilst a great deal of resources seem to be used by the mind and brain to understand the face, opinion is divided whether we genuinely develop specific skills for understanding faces, or whether face perception is just part of a general skill for making within-category discriminations, such as recognising and differentiating between similar animals or plants.

Proponents of this view argue that the differences seen between faces and non-face objects in experimental studies are due to faces being particularly difficult to distinguish. Although we often assume that faces are relatively unique, statistically they are quite similar, so a great deal of cognitive effort is needed to differentiate them. According to this view, faces are nothing more than a particularly difficult class of perceptual object which we have learned to distinguish, much as we would learn to distinguish between other similar objects if much of our communication and survival depended on it.

Artificial face perception

A great deal of effort has been put into developing software that can recognise human faces; see facial recognition system. Much of the work has been done by a branch of artificial intelligence known as computer vision which uses findings from the psychology of face perception to inform software design. See, for example, Smiling faces are better for face recognition.

References

¹Nelson, C.A. (2001) The development and neural bases of face recognition. Infant and Child Development, 10, 3-18.
²Bruce, V. & Young, A. (1986) Understanding face recognition. The British Journal of Psychology, 77 (3), 305-327.